The present invention relates generally to implantable medical electronic devices and more specifically to electrodes for nerve stimulation.
Many peripheral nerves contain fascicles which innervate antagonistic muscles. For example, the hypoglossal nerve contains fascicles innervating the genioglossus muscle which extends the tongue, and also the styloglossus muscle which retracts the tongue. In addition, many nerves to be stimulated are near other structures which must not be stimulated. Therefore, it is desirable to have an electrode array which limits the stimulus current to selected nerve fascicles.
Cuff electrodes for recording neural signals and stimulating nerve tissue are well known. For example, U.S. Pat. No. 3,774,618 issued to Avery discloses a thin, flexible strip of plastic having lead wires encapsulated in the plastic which is implanted by wrapping the plastic strip and lead wires around a single nerve.
It has also been known that a tripolar electrode arrangement confines stimulus current to the nerve cuff and that a tripolar arrangement is more selective than a monopolar arrangement (see e.g. Testerman et al., Design and Evaluation of Nerve Stimulating Electrodes, Med Res Eng 10: 6-11 1971; and Sweeney et al., A nerve cuff technique for selective excitation of peripheral nerve trunk regions, IEEE Trans Biomed Eng 37: 706-715, 1990). This selectivity can be enhanced with one or more "steering" electrodes. The electrode must also be in close contact with the nerve in order for the selectivity to work (see e.g. McNeil et al., Selective activation using peripheral nerve electrodes, Med & Biol Eng & Comput 23: 249-253, 1985). Several self-sizing cuff electrode designs have been proposed (e.g. U.S. Pat. Nos. 4,573,481; 4,602,624; and 5,095,905) but these designs tend to be fragile and difficult to install. Also important in cuff electrode design is to avoid trauma to the nerve. A half cuff design to minimize phrenic nerve trauma has been disclosed in Kim et al., Light and electron microscope studies of phrenic nerves after long-term electrical stimulation, J Neurosurg 58: 84-91, 1983.
It is therefore an object of the present invention to provide an electrode for selectively stimulating nerve fascicles.
It is also an object of the present invention to provide an electrode which is easy to secure onto a peripheral nerve.
It is also an object of the present invention to provide an electrode which minimizes trauma to the nerve.